This invention relates to an optical disk and an optical disk device for recording and reproducing high-density signals by irradiating high-energy beams such as laser beams or the like onto a thin film formed on a substrate.
Recently, optical disks on which information can be recorded and from which the information can be reproduced and erased and optical disk devices that can record information on and reproduce information from the optical disks have been commercialized. Furthermore, high-density rewritable optical disks and optical disk devices capable of recording and reproducing high-quality animation have been actively researched and developed.
Well-known rewritable optical disks include phase-change optical disks with chalcogenide thin films on a disc-shape substrate. The chalcogenide thin films comprise, for example, Gexe2x80x94Sbxe2x80x94Te, Inxe2x80x94Se, or the like. Magneto-optical recording media having metal thin films such as Fexe2x80x94Tbxe2x80x94Co as their recording layers also are well known.
In phase-change optical disks, for example, laser beams are irradiated onto and focused on recording thin films comprising the above-mentioned phase-change materials to heat the irradiated parts partially to a predetermined temperature. When the temperature of the irradiated portion becomes equal to or higher than the crystalline temperature, the irradiated portion is changed to the crystalline state. When the irradiated portion is melted at a temperature higher than its melting point and is quenched, its state is changed to the amorphous state. Once either the crystalline state or the amorphous state is determined so as to correspond to the recording state, and the other to the erasing state (unrecorded state), information can be recorded or erased reversibly by forming each state according to a pattern corresponding to information signals. Since the crystalline state and the amorphous state are different from each other in their optical characteristics, recorded signals can be reproduced by optically detecting such different characteristics as a reflectivity change or a transmittance change.
In a magneto-optical recording medium, for example, laser beams are irradiated onto and focused on a magneto-optical recording thin film to heat the irradiated portions partially to a predetermined temperature. While heating the irradiated portions, a magnetic field also is applied. The magnetizing direction of the magneto-optical recording thin film is reversed according to information, thus recording and erasing the information.
In such optical disks mentioned above, a substrate is grooved in advance so as to be provided with uneven guide grooves (hereafter also referred to as xe2x80x9cguide tracksxe2x80x9d), thus forming information tracks. In an uneven guide groove, an information track nearer to a light-incidence side is referred to as a xe2x80x9cgroovexe2x80x9d, and an information track further from the light-incidence side is referred to as a xe2x80x9clandxe2x80x9d. Information signals are recorded or reproduced by focusing laser beams on the groove or the land and scanning it. These information signals can be recorded by users themselves, thus being referred to as xe2x80x9cuser dataxe2x80x9d.
In common commercial optical disks, information signals are recorded either on a groove or on a land, and the other serves as a guard band that separates adjoining tracks.
Means for increasing recording capacity in optical disks include a technique for increasing track density by recording information signals on both groove tracks and land tracks as described in Examined Japanese Patent Application Tokkou Sho 63-57859.
In order further to increase the track density, there is a method of making the track pitch of guide tracks smaller while recording information on both the land tracks and the groove tracks mentioned above. In this case, in order to cut off the heat transfer from a track heated by laser beams to the adjacent track, a technique for making guide grooves deeper can be applied.
On the other hand, in rewritable optical disks, it is necessary to record address signals as uneven pits that indicate position information on a medium or the like in advance. As a means for recording the address signals, an intermediate address method is proposed in, for example, Unexamined Japanese Patent Application Tokkai Hei 6-176404.
An optical-beam tracking control method for reading information from an optical disk will be explained with reference to drawings as follows.
FIG. 7 is a schematic block diagram of a conventional optical disk device. An information track 501 is formed on an optical disk 500.
FIG. 8 is an enlarged view of the information track 501. The information track 501 comprises a groove track 606 and a land track 607. The information track 501 has a data area 602 for recording information and an address area (an identifying signal area) 601 in which position information of an information track and the like are recorded. The groove track 606 and the land tracks 607 are arranged alternately at an interval of a track pitch Tp. Prepits 604 of projection or pit are formed in the address area (the identifying signal area) 601. The center of a prepit 604 is arranged at a position shifted from the center of the groove track 606 in the radial direction of the optical disk by Tp/2. The arrangement of these prepits 604 enables the address signals to be reproduced from both the groove track and the land track. Generally, the depth or height of the prepits 604 is the same as the depth of the groove in the data area 602.
In FIG. 8, recording marks 605 are formed on both the groove track 606 and the land tracks 607. A beam spot 502 scans the groove track 606 and the land tracks 607 in the direction shown by an arrow.
Referring to FIG. 7, the operation during reproducing information recorded on the optical disk 500 will be explained.
A laser driving circuit 525 receives a signal L3 from a controller 518 to be changed to a reproducing mode and outputs a driving current to a semiconductor laser 510, which results in emission at a constant reproducing intensity.
As a next step, the beam-spot position in the focus direction is controlled. For this purpose, a general focus controlling method such as a spot size method or an astigmatism method may be used. Therefore, a detailed explanation of the method is not necessary herein.
A laser beam emitted from the semiconductor laser 510 provided to an optical head 514 is focused on the information track 501 by an objective lens 511. A laser beam reflected from the information track 501 enters a photodetector 512 after receiving information recorded on the information track 501 according to the reflected-light quantity distribution. Light receivers 512a and 512b comprised in the photodetector 512 convert the change in the light quantity distribution of the incident optical beam into electric signals. Each of the light receivers 512a and 512b output the electric signals to a differential amplifier 515 and a summing amplifier 521. After converting each input current into voltage, the differential amplifier 515 outputs a differential signal obtained by differentiation to a LPF (low pass filter) 516. The LPF 516 extracts a low-frequency component from the differential signal and outputs it as a signal S1 to a polarity inverting circuit 517.
The polarity inverting circuit 517 outputs a signal S2 to a tracking control circuit 519 by transmitting the signal S1 without polarity change or inverting the polarity of the signal S1 according to a control signal L1 from the controller 518. The signal S2 is a so-called push-pull signal and corresponds to a tracking error quantity between the beam spot 502 and the information track 501. In this case, when the track on which information should be recorded (or erased, hereafter the same) or from which information should be reproduced is a groove, the polarity inverting circuit 517 transmits the signal S1 without polarity change. On the other hand, when the track on which information should be recorded or from which information should be reproduced is a land, the polarity inverting circuit 517 inverts the polarity of the signal S1.
The tracking control circuit 519 outputs a tracking driving signal to an actuator driving circuit 520 according to the level of the input signal S2. The actuator driving circuit 520 outputs a driving current to an actuator 513 according to the tracking driving signal, thus shifting the objective lens 511 in the direction crossing the information track 501. This control allows the beam spot 502 to scan the center of a target groove or land of the information track.
When the beam spot 502 scans the information track 501 correctly, the quantity of the light reflected from the prepits 604 varies from the quantity of the light reflected from the recording marks 605 (see FIG. 8) due to the optical interference, thus changing the level of the output signals of the light receivers 512a and 512b. These output signals are added in the summing amplifier 521 to obtain a summed signal, and the summed signal is output to a preamplifier 522. The signal amplified by the preamplifier 522 is demodulated to reproduced data by a reproduced signal processing circuit 523. The reproduced data are output to the controller 518.
On the other hand, in recording, the laser driving circuit 525 receives a signal L3 from the controller 518 and is changed to a recording mode. At the same time, a recording signal processing circuit 524 receives a recording data signal L2 from the controller 518 and outputs a modulating signal to the laser driving circuit 525. The laser driving circuit 525 modulates the driving current output to the semiconductor laser 510 according to the modulating signal. Thus, the intensity of the beam spot 502 varies and a recording mark is formed on the information track 501.
During each operation mentioned above, a spindle motor 530 rotates the optical disk 500 at a constant angular or linear velocity.
However, in such a conventional optical disk device as described above, the polarity of the signal S1 is inverted according to the groove depth of the information track 501 and therefore tracking of a target groove track or a target land track cannot be controlled in some cases.
FIG. 9 shows the relationship between a groove depth of an information track and signal amplitude of a tracking error signal according to a push-pull method. The signal amplitude of a tracking error signal is maximum at a groove depth of xcex/8n and zero at a groove depth of xcex/4n, wherein xcex is a wavelength of a laser beam used for recording and reproduction, and n is the refractive index of a substrate. The amplitude increases when changing the groove depth from xcex/4n toward 3xcex/8n. However, the diffraction direction of a reflected light is reversed, thus reversing operating signals in the light receivers 512a and 512b. The tracking-error signal amplitude and the intensity distribution of the reflected light are repeated at a xcex/2 period. Thus, in conventional optical disk devices, the polarity of the push-pull signal, i.e. the polarity of S1 output from the differential amplifier 515 is inverted according to the groove depth of the information track 501.
In the above description, the polarity of the tracking signal is inverted at a groove depth of xcex/4n. However, the groove depth at which the polarity is inverted depends on the groove shape. That is, only when the boundary wall surface between the land track 607 and the groove track 606 of the information track 501 is perpendicular to the optical disk surface, is the tracking polarity inverted at a period of xcex/4n in groove depth. Therefore, when the boundary wall surface between the land track and the groove track is oblique to the optical disk surface, the polarity of the tracking signal is inverted at a groove depth slightly deeper than xcex/4n.
In FIG. 7, suppose that the polarity inverting circuit 517 controls the polarity of the signal S1 by transmitting the signal S1 without polarity change when scanning a groove track on the optical disk 500 having any groove depth (for example, a groove depth of xcex/6n) within the range of 0 to xcex/4n, and by inverting the polarity of the signal S1 so as to have negative polarity when scanning a land track on the optical disk 500 mentioned above.
However, when scanning an optical disk having any groove depth within the range of xcex/4n to xcex/2n in this control method, the polarity of the signal S1 is the reverse of that when scanning an optical disk having a groove depth of xcex/6n. If the switching of the tracking polarity for a groove track and a land track is controlled by the conventional control method without any change, when trying to make the beam spot 502 track the groove track, the land track is tracked. The reason is that the polarity inverting circuit 517 transmits the signal S1 without polarity change and therefore the polarity of the signal S2 becomes negative. On the other hand, when trying to make the beam spot 502 track the land track, the groove track is tracked. The reason is that the polarity inverting circuit 517 inverts the polarity of the signal S1 and therefore the polarity of the signal S2 becomes positive.
In other words, the tracking polarity in scanning a groove track and a land track is inverted according to the groove depth of the information track 501, thus causing a problem in that a target track cannot be tracked.
Such a problem hinders information from being recorded on and from being reproduced from the optical disk mentioned above in which track density is improved by recording information on both the land tracks and the groove tracks and the heat transfer to an adjacent track is controlled by making the guide-groove depth deeper.
When scanning an address area, the polarity of an output signal of the differential amplifier 515 also is inverted due to the change in height or depth of the prepits 604. Therefore, when forming the prepits 604 so as to have the same depth as that of uneven grooves in the data area 602, there has been a problem that the compatibility as to the information obtained from the address area can not be kept among disks, each of which has a different groove depth.
An object of the present invention is to solve the problems described above and to provide an optical disk and an optical disk device in which tracking of a target groove track or a target land track can be controlled regardless of the guide-groove depth by detecting the inversion in tracking polarity according to a groove depth in advance (this is hereafter referred to as a xe2x80x9cfirst objectxe2x80x9d).
Another object of the present invention is to provide an optical disk in which the reverse in recording and reproducing conditions about, for example, irradiation and a modulation pattern, and the like of a beam spot on land tracks and groove tracks can be compensated regardless of the guide-groove depth, even if tracking polarity is inverted (this is hereafter referred to as a xe2x80x9csecond objectxe2x80x9d).
Still another object of the present invention is to provide an optical disk in which the compatibility in the information obtained from an address area can be kept regardless of the groove depth of an information track (this is hereafter referred to as a xe2x80x9cthird objectxe2x80x9d).
In order to attain the first object mentioned above, optical disk devices of the present invention have the following configurations.
An optical disk device according to a first configuration of the present invention comprises a converging optical system and a tracking controller. In the converging optical system, a laser beam is irradiated onto an optical disk having a recording thin film on a substrate provided with uneven guide grooves. The tracking controller controls tracking so that the laser beam converged by the converging optical system scans a convex part or a concave part of the guide groove mentioned above. The tracking controller controls the inversion in tracking polarity according to the depth of the guide groove.
An optical disk device according to a second configuration of the present invention comprises a converging optical system, a tracking controller, a polarity inverting system, and a disk discriminating system. In the converging optical system, a laser beam is irradiated onto an optical disk having a recording thin film on a substrate provided with uneven guide grooves. The tracking controller controls tracking so that the laser beam converged by the converging optical system scans a convex part or a concave part of the guide groove mentioned above. The polarity inverting system inverts the polarity of the tracking controller. The disk discriminating system discriminates the depth of the guide grooves. According to the result obtained from the disk discrimination system, the polarity inverting system inverts the polarity of the tracking controller.
According to the optical disk device of the first or second configuration of the present invention, the tracking controller inverts the tracking polarity according to the depth of the guide groove, or the polarity inverting system inverts the polarity of the tracking controller according to the result obtained by discriminating the depth of the guide groove by the disk discriminating system. Therefore, it is possible to make a laser beam scan a target groove track or a target land track on optical disks with any groove depth correctly. Consequently, information can be correctly recorded on or reproduced from optical disks with a different guide-groove depth.
In order to attain the first object mentioned above, optical disks of the present invention have the following structures.
An optical disk according to a first structure of the present invention comprises a substrate on which uneven guide grooves are formed. The optical disk is contained in a cartridge. The cartridge is provided with identification data about the depth of the guide grooves and/or identification data about the tracking polarity of a reproducing optical system.
An optical disk according to a second structure of the present invention comprises a substrate on which uneven guide grooves are formed. In an identifying signal area provided on the optical disk, information about the depth of the guide grooves and/or information about the tracking polarity of a reproducing optical system are/is recorded.
According to the optical disks of the first and second structures mentioned above, the information about the depth of the guide grooves and/or the information about the tracking polarity of a reproducing optical system are/is recorded in the cartridge or in the identifying signal area. Therefore, since an optical disk device reads such information prior to recording or reproduction, tracking can be controlled according to the guide-groove depth. Consequently, it is possible to make a laser beam scan a target groove track or a target land track on optical disks with any groove depth correctly. Thus, information can be correctly recorded on or reproduced from optical disks with a different guide-groove depth.
An optical disk according to a third structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. Information about the tracking polarity of a reproducing optical system is recorded in a control area on the optical disk.
An optical disk according to a fourth structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. Information about the depth of the guide grooves is recorded in a control area on the optical disk.
An optical disk according to a fifth structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. The optical disk comprises address areas where positions of the guide grooves are identified. Information about the tracking polarity of a reproducing optical system is recorded in the address areas.
An optical disk according to a sixth structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. The optical disk comprises address areas where positions of the guide grooves are identified. Information about the depth of the guide grooves is recorded in the address areas.
According to the optical disks of the third to sixth structures mentioned above, in the optical disk on which guide grooves having a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n are formed, the information about the tracking polarity of a reproducing optical system or the information on the depth of the guide grooves is recorded in the control area or in the address areas. Therefore, an optical disk device reads such information prior to recording or reproduction, thus controlling tracking according to the guide-groove depth. Consequently, it is possible to make a laser beam scan a target groove track or a target land track on an optical disk with such a depth correctly. Thus, information can be recorded or reproduced correctly.
Furthermore, in order to attain the second object mentioned above, optical disks of the present invention have the following structures.
An optical disk according to a seventh structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. In the optical disk, signals are recorded on both convex parts and concave parts of the guide grooves. The optical disk is compatible with an optical disk having uneven guide grooves with a depth of at least mxcex/4n but less than (m+1)xcex/4n. The optical disk according to the seventh structure comprises a control area where convex-part recording- and reproducing-information and concave-part recording- and reproducing-information are recorded. The convex-part recording- and reproducing-information is recorded in an area where concave-part recording- and reproducing-information is recorded in an optical disk having a groove depth of at least m xcex/4n but less than (m+1)xcex/4n. The concave-part recording-and reproducing-information is recorded in an area where convex-part recording- and reproducing-information is recorded in an optical disk having so a groove depth of at least mxcex/4n but less than (m+1)xcex/4n.
An optical disk according to an eighth structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. In the optical disk, signals are recorded on both convex parts and concave parts of the guide grooves. The optical disk is compatible with an optical disk having uneven guide grooves with a depth of at least m xcex/4n but less than (M+1)xcex/4n. The optical disk according to the eighth structure comprises address areas where positions of the guide grooves are identified. Each address area comprises an area where convex-part recording- and reproducing-information is recorded and an area where concave-part recording- and reproducing-information is recorded. The convex-part recording- and reproducing-information is recorded in the area where concave-part recording- and reproducing-information is recorded in an optical disk having a groove depth of at least mxcex/4n but less than (M+1)xcex/4n. The concave-part recording- and reproducing-information is recorded in the area where convex-part recording- and reproducing-information is recorded in an optical disk having a groove depth of at least mxcex/4n but less than (M+1)xcex/4n.
According to the optical disk of the seventh or eighth structure mentioned above, recording- and reproducing-information to be recorded in the control area or in the address area is recorded in a specific area. Therefore, in an optical disk device for conventional optical disks provided with guide grooves having a depth of at least mxcex/4n but less than (M+1)xcex/4n (hereafter also referred to as a xe2x80x9cconventional optical disk devicexe2x80x9d), the conditions for recording information on and reproducing information from land tracks or groove tracks of the optical disks provided with guide grooves having a depth of at least (M+1)xcex/4n but less than (m+2)xcex/4n of the present invention can be correctly set.
In other words, when recording and reproducing information by a conventional optical disk device, the polarity of a tracking signal is inverted due to the difference in groove depth and therefore the track to be scanned is reversed. Consequently, when a groove track should be scanned, a land track is scanned, and when a land track should be scanned, a groove track is scanned. However, according to the present invention, even in such a case, recording- and reproducing-conditions of a land track or a groove track that should be actually scanned can be read correctly from the optical disks. Therefore, recording- and reproducing-conditions according to the track to be scanned are set.
As a result, information can be recorded on or recorded information can be reproduced from the optical disks of the present invention whose depth is different from that of conventional optical disks without any change in a conventional optical disk device.
In order to attain the third object mentioned above, optical disks of the present invention have the following structures.
An optical disk according to a ninth structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (M+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. In the optical disk, signals are recorded on both convex parts and concave parts of the guide grooves. The optical disk comprises address areas where positions of the guide grooves are identified. Prepits provided in the address areas have a height or depth of at least mxcex/4n but less than (m+1)xcex/4n.
According to the optical disk of the ninth structure mentioned above, the grooves of an information track have a depth of at least (M+1)xcex/4n but less than (m+2)xcex/4n, but the prepits in the address areas have a height or depth of at least mxcex/4n but less than (M+1)xcex/4n. Therefore, in a conventional optical disk device, when recording information on or reproducing information from the optical disk of the present invention, the polarity of an output signal of a differential amplifier is not inverted in the address areas. Consequently, when reading out information recorded in the address areas of the optical disk according to the present invention using a conventional optical disk device, the obtained information is compatible with the information obtained from a conventional optical disk. Thus, the information can be used without any change.
An optical disk according to a tenth structure of the present invention comprises a substrate on which uneven guide grooves are provided. The uneven guide grooves have a depth of at least (m+1)xcex/4n but less than (m+2)xcex/4n, wherein xcex is a wavelength of a laser beam used for recording or reproduction, n indicates the refractive index of the substrate, and m is 0 or a positive even number. In the optical disk, signals are recorded on both convex parts and concave parts of the guide grooves. An address area where the position of the guide groove is identified is provided between the guide grooves along a track. The address area comprises first prepits and second prepits. The first prepits are shifted to the peripheral side in the radial direction by about a xc2xd track pitch with respect to the track of the guide groove. The second prepits are shifted to the inner-circumference side in the radial direction by about a xc2xd track pitch with respect to the track of the guide groove. The sequence of the first prepits and the second prepits in a scanning direction when scanning a convex part of the guide groove right after the address area is different from that when scanning a concave part of the guide groove right after the address area.
According to the optical disk of the tenth structure mentioned above, in the case where the prepits in the radial direction are arranged reversely compared to that in a conventional optical disk provided with guide grooves having a depth of at least mxcex/4n but less than (M+1)xcex/4n, using a conventional optical disk device, it can be correctly determined whether the track following the address area is a convex part or a concave part. That is, with respect to the information indicating whether the track following the address area is a convex part or a concave part, the compatibility with a conventional optical disk can be kept.